linux-kernel - Re: [PATCH v2 01/12] sched/psi: Optimize psi_group_change() cpu

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Message-ID: <7693dedb-0185-4344-b46b-87dbf69e7ac4@meta.com>
Date: Wed, 16 Jul 2025 12:27:36 -0400
From: Chris Mason <clm@...a.com>
To: Peter Zijlstra <peterz@...radead.org>,
        Beata Michalska <beata.michalska@....com>
Cc: mingo@...hat.com, juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, vschneid@...hat.com, linux-kernel@...r.kernel.org,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH v2 01/12] sched/psi: Optimize psi_group_change()
 cpu_clock() usage

On 7/16/25 6:40 AM, Peter Zijlstra wrote:
> On Wed, Jul 16, 2025 at 08:53:01AM +0200, Beata Michalska wrote:
>> Wouldn't it be enough to use SEQCNT_ZERO? Those are static per-cpu ones.
> 
> Yeah, I suppose that should work. The below builds, but I've not yet
> observed the issue myself.

[ ... ]

>  
> -static DEFINE_PER_CPU(seqcount_t, psi_seq);
> +static DEFINE_PER_CPU(seqcount_t, psi_seq) = SEQCNT_ZERO(psi_seq);

As expected, this also works.  Thanks everyone.

-chris